The program's objectives are to: 1) isolate and characterize a mammary tumor factor(s) (MTF) which resemble epidermal growth factor (EGF) and sarcoma growth factor (SGF) from chemically-induced rat mammary tumors and from the conditioned medium of primary cultures of mammary tumor epithelial cells; 2) to determine and compare the biological, biochemical and antigenic properties of MTF to EGF and SGF; 3) to compare the effects of MTF on the growth and differentiation of normal rat mammary epithelium (RME), mouse embryonal carcinoma EC cells, and chick, mouse and rat fibroblasts and 4) to delineate the relationship of MTF production in preneoplastic cells and primary and transplantable hormone-dependent and independent tumors to tumor promotion and growth.